Processing using laser light is carried out by use of a configuration wherein laser light divergently emitted from an end face of an optical fiber is collimated and thereafter the collimated laser light is condensed by using a condensing lens, to focus the laser light at a point on a workpiece. When the laser light is multicolor light with a wide spectral width such as white light, the focal length differs depending upon the wavelengths of the light. Due to it, a position (beam waist) where the light emitted from the end face of the optical fiber becomes a plane wave after collimated, with respect to the end face of the optical fiber also differs depending upon the wavelengths of the light, and thus it is difficult to focus wavefronts of the multicolor light at one point. Therefore, the conventional laser processing technology is designed to use an achromatic lens as the condensing lens, thereby to reduce chromatic aberration.